Bar chart fixes and help page

[HenrikeW]

Related issue(s) and PR(s)

This PR closes #612, closes #619 and closes #620.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

List of changes made

• the time span for the bar chart was extended to the full current year
• the heading for the bar chart was changed
• a section for the bar chart on the help page was added

Screenshot of the fix

Testing

• Go to the report page and log some time during different times. Only time entries between Jan 1st 2022 and Dec 31st 2022 should be represented in the chart.
• Read the help page section and check if it's complete, correct and understandable.

Further comments

Definition of Done checklist

• I have made an effort making the commit history understandable
• I have performed a self-review of my own code and commented any hard-to-understand areas
• Tests and lint/format validations are passing
• My changes generate no new warnings

[jonandernovella]

Looks good! I left a few suggestions to improve the help page.

[KattisLej]

Looks good